Inflammation is characterized by the recruitment of phagocytes from the blood stream, the adhesion of these cells to extracellular matrices, and the functional activation and secretion of microbicidal and cytotoxic products. However, our understanding of the interrelatedness of these processes is quite limited. Recent studies have shown that adherent neutrophils and monocytes activated by inflammatory agents aggressively produce hydrogen peroxide. We have recently demonstrated, by a quantitative method developed in this laboratory, that these cells also produce singlet oxygen. The production of these reactive oxygen species (ROS), particularly singlet oxygen, are an important part of the phagocyte arsenal against invading microorganisms and are thought to be of prime importance in inflammatory responses, in conjunction with proteolytic enzymes released by the activated cells. In diseases associated with bone or dentin surfaces, the recruitment of monocytes from the circulation and increased osteoclast formation results in an increased loss of extracellular calcified matrix at these sites. It has been suggested that in addition to the recruited monocytes, osteoclasts are also capable of producing superoxide when attached to bone surfaces, and that ROS are themselves involved in the process of bone resorption. This proposal is thus divided into four general areas: 1) biochemical guantitation of the ROS, particularly singlet oxygen, produced by neutrophils, monocytes, and osteoclasts, adhered to extracellular matrix proteins or devitalized bone surfaces and stimulated with inflammatory mediators; 2) cytochemical localization of ROS production sites in adherent cells and cell populations within calvarial bone culture; 3) determine the oxygenase(s) or peroxidases involved in the production of the ROS, particularly singlet oxygen, which include: NADPH-oxidase, 5-lipoxygenase, myeloperoxidase, and cyclooxygenase and by preparing cell-free systems to determine the amount of NAD(P)H-oxidase or other oxidase activity these cells contain, and 4) pathophysiological importance of the ROS in mediating bone resorption by measuring the release of bone mineral and determining structural or functional changes or increased susceptibility of the ROS exposed extracellular matrix proteins to proteolytic degradation. Information obtained from these studies will add significantly to our understanding of the role ROS play in the pathophysiology of inflammation associated several disease states, such as periodontal disease and inflammatory mediated bone resorption.